WANG Lei, ZHANG Qiongwan, LI Weibiao. Diagnosis of the ENSO modulation of tropical cyclogenesis over the southern South China Sea using a genesis potential index[J]. Acta Oceanologica Sinica, 2012, (5): 54-68. doi: 10.1007/s13131-012-0236-6
Citation:
WANG Lei, ZHANG Qiongwan, LI Weibiao. Diagnosis of the ENSO modulation of tropical cyclogenesis over the southern South China Sea using a genesis potential index[J]. Acta Oceanologica Sinica, 2012, (5): 54-68. doi: 10.1007/s13131-012-0236-6
WANG Lei, ZHANG Qiongwan, LI Weibiao. Diagnosis of the ENSO modulation of tropical cyclogenesis over the southern South China Sea using a genesis potential index[J]. Acta Oceanologica Sinica, 2012, (5): 54-68. doi: 10.1007/s13131-012-0236-6
Citation:
WANG Lei, ZHANG Qiongwan, LI Weibiao. Diagnosis of the ENSO modulation of tropical cyclogenesis over the southern South China Sea using a genesis potential index[J]. Acta Oceanologica Sinica, 2012, (5): 54-68. doi: 10.1007/s13131-012-0236-6
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;State Key Laboratory of Satellite Ocean Environmental Dynamics, Second Institute of Oceanography, State Oceanic Administration, Hangzhou 310012, China;Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
2.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China;Institute of Tropical and Marine Meteorology, China Meteorological Administration, Guangzhou 510058, China
3.
Department of Atmospheric Sciences, School of Environmental Science and Engineering, Sun Yat-sen University, Guangzhou 510275, China
The modulation of tropical cyclogenesis over the southern South China Sea (SSCS) by the El Niño-Southern Oscillation (ENSO) is examined in October-December (OND), when tropical cyclone (TC) activities are most active in this region. The results reveal that there were more TCs formed over the SSCS during La Niña years and less TCs during El Niño years. How different environmental factors (including low-level vorticity, mid-level relative humidity, vertical wind shear, and potential intensity) contribute to this influence is investigated, using a genesis potential (GP) index developed by Emanuel and Nolan. Composite anomalies of the GP index are produced for El Niño and La Niña years separately, which could account for the changes of TC frequency over the SSCS in different ENSO phases. The degree of contribution by each factor is determined quantitatively by producing composites of modified indices in which only one of the contributing factors varies, with the others set to climatology. The results show that the mid-level relative humidity makes the largest contribution to the ENSO modulation of tropical cyclogenesis over the SSCS. Although warmer sea surface temperatures (SSTs) and larger amount of evaporation from the ocean surface were observed over the SSCS during El Niño years, anomalous descending motions due to the anomalous Walker circulations inhibited the upward transports of water vapor and led to less moisture contents in the middle troposphere, which suppressed TC formations.
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